1. Field of the Invention
The invention discloses a method for mixing light, particularly a methodology for multispectral mixing optimization of LEDs clusters.
2. Description of the Prior Art
The progress in Light-emitting diodes (LEDs) technology has been breathtaking during the last few decades. At this time, great technological advances in LEDs are profoundly changing the way light was generated. In contrast to many conventional light sources, LEDs not only have the potential of converting electricity to light with near-unit efficiency, but also offer impressive controllability of their spatial distribution, temporal modulation, and polarization property. With an arrangement of multispectral LEDs, the LEDs cluster could particularly have the capability of manipulating its synthesized spectral power distributions (SPDs). Such intelligent light sources could be adjusted according to different operational environments and requirements. As a result, tremendous properties of LEDs or LEDs cluster lead to great benefits across a wide field of applications, including lighting, transportation, communication, imaging, agriculture, and medicine.
In general, the mixing of multiple spectra based on LEDs can be accomplished by using (i) additive mixing of two or more single-color LED chips (LED-primary-based approach), (ii) wavelength-conversion via using phosphors or other materials (LED-plus-phosphor-based approach), and (iii) a hybrid approach composed of (i) and (ii). It is well known that a basic trichromatic mixing by LED-primary-based approach is mathematically critical determined, in which the three emission sources are predetermined. In fact, the selections of emission band {circumflex over (λ)} provide additional degrees of freedom, whose values will be highly relevant to the operational purposes. For example, a trichromatic combination of {circumflex over (λ)}=450-455 nm (spectral width Δλ=5 kT), {circumflex over (λ)}2=525-535 nm (Δλ=5 kT), and {circumflex over (λ)}2=600-615 nm (Δλ=5 kT) is very favorable in terms of high color rendering lighting, resulting in a high CRI value in the range of 80-85.
It is generalized that the condition by considering a synthesized SPD composed of n undetermined emission bands, used for certain purpose with specific chromaticity point. The problem is no longer critically determined but underdetermined, which is equivalent to subjecting the 2n-dimensional parameter space {{circumflex over (λ)}1, . . . , {circumflex over (λ)}n, I1, . . . , In}, composed of emission bands {circumflex over (λ)} and drive currents I, to three color-mixing constrains. In other words, an optimization happens in searching the best location, composed by two n-dimensional vectors {{circumflex over (λ)}1, . . . , {circumflex over (λ)}n} and {I1, . . . , In}, on the hypersurface with dimensionality 2n−3. Where the best location represents that composed spectrum provides the maximal benefit to the purposes. It could mathematically write the solution in a form as:arg max[{MF,cons}{{circumflex over (λ)}1, . . . ,{circumflex over (λ)}n,I1, . . . ,In}]where MF is the merit function of the purposes. The term cons indicates three mixing constrains. In 2002, A. {hacek over (Z)}ukauskasa et al. solved the above problem for general lighting applications. For simplicity, each emission band was assumed as a single Gaussian line with Δλ=6 kT. The optimal LEDs clusters for n=2, 3, 4, and 5 were analyzed. Those results address the fundamental tradeoff between the luminous efficacy of radiance LER and the color rendering index CRI, which has the potential to provide a useful guide in the design of a polychromatic system.
However, as the trend of higher efficiencies in phosphor-converted white LEDs continues, the possible hybrid designs increases as well. State of the art tetrachromatic hybrid design (neutral-white/red/green/blue), proposed by G. He et al., can realize a white composite light with high color rendering property as well as high luminous efficiency, but due to the assumption of constant thermal environment (i.e. only consider the dependence of current on source model) a widespread diffusion of multichip LED cluster is not provided. To date, a general SPD synthesizing for practical LED clusters, especially for those with the number of sources >3, is still subject of discussion. Main obstacle lies in the present lack of complete methodology, which can systematically and efficiently optimize SPD for an underdetermined system in consideration of current and temperature dependences
In order to overcome current implementation barriers of LEDs cluster, we make an attempt to borrow design techniques from a conventional lens system to develop a general mixing approach in a more complete treatment. The idea arose from the recognition of the fundamental similarity of multi-chip LEDs system and conventional lens system. The whole design flow in all aspects can be closely analogous to a lens design process that has long been developed, by which the spectrum of an LED cluster can be optimized by going through every step of the proposed scheme.